Note 11 - Net Income Per Share - Basic and Diluted Net Income Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Net income	$ 11,704	$ 10,467	$ 33,097	$ 30,411
Basic (in shares)	22,542	22,385	22,524	22,325
Dilutive securities (in shares)	422	418	460	386
Average shares outstanding including dilutive securities including dilutive securities (in shares)	22,964	22,803	22,984	22,711
Basic (in dollars per share)	$ 0.52	$ 0.47	$ 1.47	$ 1.36
Diluted (in dollars per share)	$ 0.51	$ 0.46	$ 1.44	$ 1.34